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Modification of the spectra of correlated charm anti-charm quark pairs in the Quark-Gluon Plasma
Ismat Ullah, Min He
Published:   , doi: 10.1088/1674-1137/44/5/054102
Heavy quarks play an important role in probing the properties of strongly interacting quark-gluon plasma (QGP) created in ultra-relativistic heavy ion collisions. We have studied the interactions of single heavy (charm) quarks and correlated charm and anti-charm (\begin{document}$c\bar c$\end{document}) quark pairs with medium constituents in QGP by performing fireball + Langevin simulations of pertinent Brownian motion through elastic collisions. Besides studying traditional observables like nuclear modification factor and elliptic flow for single heavy quark motion inside QGP at different values of thermal relaxation rate, we have also scrutinized the broadening of azimuthal correlations distributions among charm and anti-charm quark pairs in the QGP medium at different relaxation rates and different transverse momenta classes. We have quantified smearing of \begin{document}$c\bar c$\end{document} pair azimuthal correlations with increasing thermal relaxation rate: while the (nearly) back-to-back correlations among \begin{document}$c\bar c$\end{document} pairs are almost completely washed out at low transverse momentum (pT), these correlations at higher pT could largely survive the evolution. This provides a novel observable of diagnosing the properties of QGP.
Probe Chiral Magnetic Effect with Signed Balance Function
A. H. Tang
Published:   , doi: 10.1088/1674-1137/44/5/054101
In this paper a pair of observables are proposed as alternative ways, by examining the fluctuation of net momentum-ordering of charged pairs, to study the charge separation induced by the Chiral Magnetic Effect (CME) in relativistic heavy ion collisions. They are, the out-of-plane to in-plane ratio of fluctuation of the difference between signed balance functions measured in pair’s rest frame, and the ratio of it to similar measurement made in the laboratory frame. Both observables have been studied with simulations including flow-related backgrounds, and for the first time, backgrounds that are related to resonance's global spin alignment. The two observables have similar positive responses to signal, and opposite, limited responses to identifiable backgrounds arising from resonance flow and spin alignment. Both observables have also been tested with two realistic models, namely, a multi-phase transport (AMPT) model and the anomalous-viscous fluid dynamics (AVFD) model. These two observables, when cross examined, will provide useful insights in the study of CME-induced charge separation.
Quasinormal modes of charged black holes in Einstein-Maxwell-Weyl gravity
De-Cheng Zou, Chao Wu, Ming Zhang, Ruihong Yue
Published:   , doi: 10.1088/1674-1137/44/5/055102
By adopting test scalar field perturbation, we study the quasinormal modes (QNMs) of charged black holes in the Einstein-Maxwell-Weyl (EMW) gravity. We find that the imaginary part of QNM frequencies is always negative for different angular parameter l, thus impling that these modes always decay and are therefore stable. In addition, we don’t observe any good linear relation between ω and p for these charged black holes, because the charge Q brings about nonlinear effect. We have also evaluated the massive scalar field perturbation against the charged black holes, and found that the random long lived modes (so-called quasiresonances) would be able to exist in this spectrum.